The subject matter disclosed herein relates to a combined cycle power plant and, more particularly, to the heat recovery boiler with enhanced heat transfer surface area for improved combined cycle performance and economics. The subject matter applies to a single shaft, combined cycle power plant, a multi-shaft, combined cycle power plant and a cogeneration power plant. In addition the subject matter may be applicable to natural circulation, forced circulation and once through heat recovery boilers configured with horizontal and/or vertical heat transfer tubes with gas turbine exhaust flow in either a horizontal and/or vertical direction. The heat recovery boiler tube arrangement may be in-line or staggered and the heat recovery boiler may be unfired or supplementary fired.
Combined cycle power plants utilize at least one gas turbine, at least one steam turbine and heat recovery boilers in combination to produce electricity and/or to process steam. The power plant is arranged such that the gas turbine is thermally connected to the steam turbine and/or process steam system through a heat recovery boiler such as a Heat Recovery Steam Generator (“HRSG”). The HRSG is essentially a large duct with water/steam filled heat exchanger tube bundles interposed therein. Feed water enters an economizer and circulates through the tube bundles such that the water is converted to steam as the gas turbine exhaust gas passes through the duct and over the tube bundles. The combined cycle power plant derives its thermal efficiency from the use of the heat rejected from the gas turbine as a supply of energy for the steam bottoming cycle (steam turbine and/or process steam). The performance and economics of the HRSG is directly related to the efficiency of heat transfer between the gas turbine exhaust gas (hot side) and the water/steam in the tube bundles (cold side). HRSGs typically utilize finned type tubes (solid and serrated) to enhance the rate of heat transfer from the gas turbine exhaust gas to the water/steam in the tube bundles however, overall heat transfer is limited by the heat transfer surface area which is located within the duct of the HRSG and the need to maintain reasonable flow characteristics and pressure drop of the gas turbine exhaust gas.
It is therefore desired to provide a combined cycle power plant that is configured to have increased performance and economics through the improvement of heat transfer in the HRSG.